Gas phase reactions for the production of olefin polymers are well known in the art. Such gas phase reactions are typically carried out in fluidized bed and stirred or paddle-type reaction systems. These reactions can be used to produce polyolefins which are homopolymers, copolymers, and terpolymers of alpha olefins and may optionally contain dienes, aromatic compounds with vinyl unsaturation and/or carbon monoxide.
In these reactions, a catalyst is required to cause polymerization of the one or more alpha olefin monomers having 2 to 12 carbon atoms, and the optional dienes, to take place. Such catalysts can include, but are not limited to, coordinated anionic catalysts, cationic catalysts, free-radical catalysts, anionic catalysts, and the like. In commercial production, such catalysts are generally introduced into the reaction zone as solid particulates in which the catalytically active material is impregnated in an inert support. As used herein, the term "inert" modifying a particular material such as a catalyst support or solvent, means that the material being referred to is non-deactivating in the reaction zone under the conditions of the gas phase polymerization process and is non-deactivating with the catalyst in or out of the reaction zone.
Conventionally, for polymerization of monomers to sticky polymers as in U.S. Pat. No. 4,994,534, particularly ethylene/propylene rubbers (EPRs) which include ethylene/propylene copolymers (EPMs) and ethylene/propylene/diene terpolymers (EPDMs), in the gas phase, the catalyst is impregnated in an inert support so as to facilitate control of polymer particle size which in turn controls the fluidization properties and the bulk density of the polymer product. The polymerization, utilizing an inert particulate material such as carbon black as a fluidization aid to reduce stickiness in the final polymer, is conducted above the softening or sticking temperature of the sticky polymer being formed.
Until recently, those skilled in the art believed that, for polymerization reactions, particularly gas phase polymerization reactions, it is necessary to provide a solid catalyst or a catalyst impregnated in an inert support so as to facilitate control of polymer particle size and thereby control the product polymer morphology and bulk density. U.S. Pat. No. 5,317,036, discloses the use of unsupported, soluble olefin polymerization catalysts having a droplet size ranging from about 1 to about 1,000 microns as useful in gas phase reactions and that they can be introduced into the reaction zone in liquid form. Examples 16-19 of this patent disclose the use of a metallocene catalyst in liquid form with carbon black to produce EPDM in a horizontally mixed batch reactor system.
introduction of a catalyst into the reaction zone in liquid form provides a catalyst activity equal to or even greater than that found with supported catalysts. In a fluid bed polymerization reaction, control of the polymer average particle size is required to maintain a continuous sustained reaction. The average particle size is the average size of the distribution of the particles employed. When the average particle size is too small, the particles are carried over into the cycle piping where fouling of the system occurs. When the polymer particles are allowed to grow too big, then it becomes impossible to fluidize the particles, heat transfer is lost, and the bed agglomerates. There is an on-going need to be able to regulate or control particle growth of the final polymer product.